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Ch. 12 - The Cell Cycle
Campbell - Campbell Biology 11th Edition
Urry11th EditionCampbell BiologyISBN: 9789357423311Not the one you use?Change textbook
All textbooksUrry 11th EditionCh. 12 - The Cell CycleProblem 4
Chapter 12, Problem 4

The decline of MPF activity at the end of mitosis is due to
a. The destruction of the protein kinase Cdk
b. Decreased synthesis of Cdk
c. The degradation of cyclin
d. The accumulation of cyclin

Verified step by step guidance
1
Understand the role of MPF (Maturation Promoting Factor) in the cell cycle. MPF is a complex of cyclin and Cdk (Cyclin-dependent kinase) that is crucial for the progression of cells from G2 phase to mitosis.
Recognize that MPF activity is regulated by the concentration of cyclin. Cyclin binds to Cdk, activating it, which in turn promotes mitosis.
Identify that at the end of mitosis, MPF activity must decline to allow the cell to exit mitosis and enter the next phase of the cell cycle.
Learn that the decline in MPF activity is primarily due to the degradation of cyclin. Cyclin is tagged for destruction by ubiquitination, leading to its breakdown by proteasomes.
Conclude that the degradation of cyclin results in the inactivation of Cdk, as Cdk requires cyclin to be active. Therefore, the correct answer is related to the degradation of cyclin.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

MPF (Maturation Promoting Factor)

MPF is a complex of cyclin and cyclin-dependent kinase (Cdk) that plays a crucial role in regulating the cell cycle, particularly the transition from G2 phase to mitosis. Its activity is essential for the initiation of mitosis, and it is regulated by the levels of cyclin and the phosphorylation state of Cdk.
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Cyclin

Cyclins are proteins that control the progression of cells through the cell cycle by activating Cdks. Cyclin levels fluctuate throughout the cell cycle, with specific cyclins being synthesized and degraded at different stages, which in turn regulates the activity of Cdks and the timing of cell cycle events.

Cyclin Degradation

The degradation of cyclin is a key mechanism for regulating MPF activity. At the end of mitosis, cyclin is targeted for degradation by the ubiquitin-proteasome pathway, leading to a decrease in MPF activity. This degradation is crucial for the exit from mitosis and the transition to the next phase of the cell cycle.
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Related Practice
Textbook Question

Through a microscope, you can see a cell plate beginning to develop across the middle of a cell, and nuclei forming on either side of the cell plate. This cell is most likely

a. An animal cell in the process of cytokinesis

b. A plant cell in the process of cytokinesis

c. A bacterial cell dividing

d. A plant cell in metaphase

Textbook Question

Vinblastine is a standard chemotherapeutic drug used to treat cancer. Because it interferes with the assembly of microtubules, its effectiveness must be related to

a. Disruption of mitotic spindle formation

b. Suppression of cyclin production

c. Myosin denaturation and inhibition of cleavage furrow formation

d. Inhibition of DNA synthesis

Textbook Question

One difference between cancer cells and normal cells is that cancer cells

a. Are unable to synthesize DNA

b. Are arrested at the S phase of the cell cycle

c. Continue to divide even when they are tightly packed together

d. Cannot function properly because they are affected by density-dependent inhibition

Textbook Question

In the cells of some organisms, mitosis occurs without cytokinesis. This will result in

a. Cells with more than one nucleus

b. Cells that are unusually small

c. Cells lacking nuclei

d. Cell cycles lacking an S phase

Textbook Question

Which of the following does not occur during mitosis?

a. Condensation of the chromosomes

b. Replication of the DNA

c. Separation of sister chromatids

d. Spindle formation

Textbook Question

Cell A has half as much DNA as cells B, C, and D in a mitotically active tissue. Cell A is most likely in

a. G1

b. G2

c. Prophase

d. Metaphase